December 17, 2016, by Tim Radford
Iceberg in the Weddell Sea: A warmer world can expect more bergs.
Image: Courtesy of Mike Weber
Scientists now believe that the East Antarctic ice sheet could become unstable, a discovery with potentially serious global implications.
LONDON, 17 December, 2016 – East Antarctica, the supposedly stable sheet of ice that makes up the greater part of the Southern Continent, may not be so stable after all. Scientists from the Netherlands have identified a mechanism that can trigger melting deep in the huge ice shelf.
And an international team of researchers has found that the planet’s single greatest body of ice is not just vulnerable to disintegration, but has played a dynamic role in natural climate change for at least 8,000 years.
The continent carries most of the world’s fresh water in the form of ice: if it all melted, sea levels would rise by 60 metres or more. But the process would take millennia and anyway, the latest research does not suggest that the East Antarctica ice sheet is unstable: just that, like the fast-warming West Antarctica region, it could become unstable.
Researchers from the Belgian university KU Leuven, but working in Holland, report in Nature Climate Change that a combination punch of wind action and sunlight had created a crater in the East Antarctic ice shelf, a crater that filled with meltwater, became a lake, collapsed and drained away to the sea below.
Strong and persistent winds delivered dry air, which blew away the snow, to darken the surface so that the shelf absorbed more solar radiation, to create a microclimate hotspot. The discovery was a surprise: the phenomenon has been observed in Greenland, but never before on an ice shelf.
Ice shelves maintain the stability of the ice on the continent: a huge ice shelf slows glacial flow from the highlands and effectively constrains the flow of meltwater. So the discovery is ominous.
“Tens of metres of rising sea levels are locked away in Antarctica,” said Jan Lenaerts, now also at Utrecht University in Holland. “And our research has shown that East Antarctica is also vulnerable to climate change.”
The region is vast, and inaccessible for most of the year. In a world in which the combustion of fossil fuels is raising levels of greenhouse gases in the atmosphere, to ramp up global warming and trigger climate change, the stability of the world’s last and largest pristine body of ice is always in question.
But, vulnerable or not, the Antarctic ice sheet is part of the climate machine, and scientists from Europe, the US and New Zealand report in Nature that they think they have worked out how. They read a story of melting and freezing in sand grains delivered by icebergs to the ocean floor.
“Virtually all the climate models had the Antarctic ice sheet as a constant entity,” said Pepijn Bakker, of the Centre for Marine and Environmental Sciences in Bremen, Germany. “It was a static blob of ice, just sitting there. What we discovered, however, is that the ice sheet has undergone numerous pulses of variability that have had a cascading effect on the entire climate system.”
As ocean temperatures warm, the ice sheet melts below the surface, and more icebergs break off. But the influx of cold fresh water from melting icebergs then lowers the ocean salinity and cools surface temperatures, allowing the surface to freeze more easily.
“Meltwater from the Antarctic won’t just raise global sea level, but might also amplify climate changes around the world”
This acts as what engineers call “negative feedback” and would explain the paradox of more extensive southern ocean ice in a warming world. The Antarctic ice shelf becomes part of the climate system that keeps Antarctica cold.
“This response is well known, but what is less known is that the input of fresh water also leads to changes far away in the northern hemisphere, because it disrupts part of the global ocean circulation,” said Nick Golledge from Victoria University in Wellington, New Zealand, an ice-sheet modeller and co-author.
“Meltwater from the Antarctic won’t just raise global sea level, but might also amplify climate changes around the world. Some parts of the North Atlantic may end up with warmer temperatures as a consequence of part of Antarctica melting.” – Climate News Network
Tim Radford, a founding editor of Climate News Network, worked for The Guardian for 32 years, for most of that time as science editor. He has been covering climate change since 1988.